The present invention relates to a pneumatic shaft assembly of machine tool.
As shown in FIGS. 1 and 2, the U.S. Pat. No. 3,776,609 discloses a pneumatic shaft bearing assembly having a shaft 1 received in a sleeve 2 which is secured firmly to a housing 3 and provided on the external surface thereof with an annular groove 4. There are two sets of balancing rooms 5 and 6 located equidistantly to the left and the right of the annular groove 4. Each of the balancing rooms 5 and 6 is provided with the two bores 7 and 8 communicating with the interior of the sleeve 2 and with the annular groove 4 via two channels 9 and 10. The wall of the housing 3 has an opening 11 in communication with the annular groove 4 so as to permit the compressed air to enter the sleeve 2 via the opening 11, the annular groove 4, the channels 9 and 10, and the bores 7 and 8. The compressed air exerts a lateral balancing force on the shaft 1 so that the shaft 1 rotates or moves axially inside the sleeve 2 with a minimum of frictional force.
The prior art shaft assembly described above is defective in design in that the entry of the compressed air into the sleeve 2 can be obstructed by the channels 9 and 10 clogged by dust or foreign objects. In addition, the construction of such channels increases the overall cost of making the shaft assembly.